Licensing FAQ

Why is PJSIP licensed as GPL and not (LGPL|Apache|BSD|choose your OSS license here)?

Basically we agree with FSF on this issue. Quoting the GPL FAQ:

• Q: Why should I use the GNU GPL rather than other free software licenses?

• A: Using the GNU GPL will require that all the released improved versions be free software. This means you can avoid the risk of having to compete with a proprietary modified version of your own work.

We don’t want people to take PJSIP, mess it up (erm, improve it), and keep the improvements as proprietary code. On the contrary, we want everybody to enjoy PJSIP and all its improvements, and the only way to make sure of this is by releasing PJSIP as GPL. Sure this still leaves some debate over why not use, say LGPL, but I guess this page is probably too short to cover that. Our stand on LGPL is explained much better here.

What about the “viral” nature of the GPL?

People often think that using GPL-ed software means that other software linked with the GPL software have to be GPL too, hence GPL is considered as viral. That is not exactly true. Don’t forget that GPL is compatible with many other free software licenses, including:

• Public domain

• Berkeley Database License,

• eCos license version 2.0,

• Modified BSD license (the original BSD license modified by removal of the advertising clause, sometimes is referred to as the 3-clause BSD license),

• Expat License,

• FreeBSD license,

• X11 License, and of course,

• GNU LGPL.

And don’t forget that the PJSIP license is GPLv2 or later, which means one can use PJSIP under GPLv3, which is compatible with even more licenses such as:

• Apache License Version 2.0 and

• Microsoft Public License (Ms-PL).

For more complete list of licenses that are compatible with GPL, please see http://www.gnu.org/licenses/license-list.html.

In addition, we specifically allow linking PJSIP with some open source third party libraries, as they are listed in Third Party SOFTWARE.

Can I develop closed source products with PJSIP?

It depends. We use the standard GPL v2 or later for PJSIP, and GPL does allow using GPL-ed code for closed source development, as long as the resulting product is not redistributed (for example, it is only used for internal purpose). Please see GPL FAQ for more information about what can/can’t be done with GPL software.

Alternatively, PJSIP can be used with Alternative license.